The invention relates to a rotor for a dynamoelectric machine such as an electric generator, according to the kind as defined in closer detail in the preamble of claim 1.
For the purpose of fastening winding heads of rotor windings it is common practice among other things to support the winding heads on the inside by an annular winding head carrier and to fix the winding heads to said winding carrier by means of binding bands. Especially in the case of larger machines it is also possible to use a ring divided several times instead of a binding band, which ring rests with intermediate insulating layers on the winding heads and is fixed by means of screws to the winding carrier. Caps can also be slid over the winding heads in the case of especially large centrifugal forces. Such caps are especially used for fixing the winding heads of rotors of turbogenerators (see book “Leitfaden der Elektrotechnik” (Electrical Engineering Guide), Vol. 3, “Konstruktions-und Festigkeitsberechnungen elektrischer Maschinen” (Calculations of Construction and Strength of Electrical Machines), author: Dr. C. von Dobbeler, 1962, B. G. Teubner Verlagsgesellschaft Stuttgart, pp 25 to 29 and 58 to 62, DE 26 29 574 B2; DE-PS 7 01 612). It is further known to absorb the centrifugal forces originating from the revolving excitation coil of a synchronous machine with the help of holding bridges resting on the outer face side of the excitation coil, which holding bridges are held on their part by bolts which are subjected to tension and are fastened to the running body of the machine (DE-PS 9 50 659).
The task of Fixing winding heads of a rotor applies especially in rotor-fed slip-ring machines, as are used for speed-controllable hydraulic-power motor generators for pumped-storage operation. It is characteristic for such generator motors among other things that the rotor can have a diameter of 3 to 8 m. It is known for fixing the winding heads of such a rotor to arrange holding rings via trestles on the rotor body, in which the ends of U-shaped tie-bolts are fixed. One respective tie-bolt grasps with its U-shaped end over a winding head (Report 11-104 “Development and achieved commercial operation . . . , for a pumped storage power plant”, of CIGRE Conference 1992, 30 Aug. to 5 Sep., JP 08-0908444 A). Such winding head fixing is very complex from a constructional and mounting viewpoint.
DE 195 19 127 C1 describes a dynamoelectric machine of the kind mentioned above. The securing device against centrifugal forces comprises tie rods which act with their radially inner ends on the support ring and with their radially outer ends on bearing boxes which rest on the winding heads radially on the outside.
The winding heads are current-carrying. They are therefore heated to higher temperatures and expand. The support ring on the other hand is not current-carrying and therefore remains cold. In order to prevent mechanical tensions resulting therefrom, cooling air is supplied to the air gap between the support ring and the winding heads, mostly from the face side of the machine. The cooling air enters the radial gap between the winding heads, flows through said winding heads in the radial direction and exits again outside of the winding heads. Practice has shown that this kind of cooling is insufficient when the bearing boxes—as in the aforementioned German specification—are comparatively large and substantially cover the circumferential area of the winding head.
A configuration is therefore known from DE 195 13 457 A1 which comprises radially extending openings in the region of the winding head carrier which is disposed adjacent to the rotor body in order to allow cooling air to flow into the region of the winding head. In order to ensure sufficient through-flow, support bodies are connected via tie rods with a support ring in the region of the winding head carrier for the purpose of supporting the winding head against centrifugal forces. Said support bodies are provided with a comparatively small configuration and are arranged in a distributed manner over the winding elements extending in the region of the winding head largely at an angle in relation to the axial direction.
Although the described configuration allows better cooling of the winding elements in the region of the winding head, it has an exceptionally overall size because sufficient space for radially guiding the tension bolts between the individual winding elements needs to be provided. Furthermore, it shows decisive disadvantages in air resistance. The support bodies which are distributed in a very numerous way and with large distance with respect to one another over the winding head produce high amounts of swirling of the air with a resulting high air resistance, especially in the case of rapidly running machines.